1. Field of the Invention
The present invention relates to a pole of plastic material which is primarily intended to support electric power transmission lines and is reinforced by a wound structure of fibers or so-called filaments disposed tangentially with respect to the principal axis.
The invention is also directed to a device for forming a filament-wound structure on said pole.
2. Description of the Prior Art
Poles of plastic material filled with glass fibers extending in the longitudinal direction of the pole are already known. The cross-sectional area of the pole decreases from the lower end to the upper end as a function of the bending moment which typically appears in poles of this type.
As a general rule, power-line poles of the type just mentioned are thus of frusto-conical shape.
Known power poles of plastic material which fall into the same class but are constructed in accordance with a different design are reinforced externally by a filament-wound structure. In the known designs, the filament-winding operation is performed by means of a filament web impregnated with resin in the unpolymerized state, the filament web being fed to the frusto-conical pole at a predetermined angle with respect to this latter by driving the pole in rotation about its axis and by subjecting the filament web to a displacement along the pole from the lower end to the upper end in a direction parallel to the axis of the pole while this latter is being driven in rotation. In the known designs, the filament winding forms a constant pitch from one end of the pole to the other, with the result that the filament density is uniformly distributed over the entire length of the pole.
The fibers constituting a filament are strongly bonded to the plastic pole by polymerization of the resin with which said fibers are coated.
As disclosed in German patent Application No. 3,039,141 filed by Vulkan Werk, another known type of plastic pole was proposed in particular for supporting electric power transmission lines and was reinforced by a filament-wound structure. In this case the density of fibers of the winding decreased progressively from the bottom to the top of the pole. In accordance with the teachings of this patent Application, however, the pole is made up of pole elements assembled together in end-to-end relation and the filament winding serves essentially to carry out interassembly of pole elements placed end to end.